1. Field of the Invention
The present invention relates to an organic EL (Electro-luminescent) display device operating based on an electro-luminescent phenomenon and a method for manufacturing a same and more particularly to the organic EL display device in which a hygroscopic agent is enclosed_hermetically and a method for manufacturing a same.
The present application claims priority of Japanese Patent Application No. Hei 11-374834 filed on Dec. 28, 1999, which is hereby incorporated by reference.
2. Description of the Related Art
An EL display device using an electroluminescent phenomenon, since it has various advantages in that it can be configured so as to be of a spontaneous light-emitting type and of a thin flat-panel type, that it draws less power, that it can provide better viewability and fast responsivity and that it can display moving images, is considered to be promising for wider applications. Two types of EL display devices are known, one being an inorganic EL display device employing inorganic materials and another being an organic EL display device employing organic thin films. In recent years, since various organic luminescent compounds have been developed which enable light-emitting in multiple colors and allow a full color EL display device to be implemented, development of the organic EL display device is being promptly pursued. Such the organic EL display device is fabricated based on a phenomenon in which light is emitted when a hole injected from an anode and an electron injected from a cathode are recombined in a light-emitting layer composed of an organic luminescent substance having a fluorescent capability contained in an organic thin-film sandwiched between the anode and the cathode, that is, when they are changed from an excited state to a deactivated state. Moreover, recent prompt advancement of the EL display device is also attributable to greatly improved light-emitting efficiency and luminance achieved by employing a structure in which hole transporting layers and/or electron transporting layers are stacked as the light-emitting layer.
Though improvements have been made to increase its display life to a considerable extent, there are still left many factors of deterioration including occurrence of a dark spot being a region where no light is emitted, and sufficiently satisfactory display life has not yet been implemented. One of the factors of deterioration is an influence of moisture which is a problem specific to organic thin-film materials. That is, the organic EL device using such organic thin-film materials is easily affected by moisture existing in an area surrounding the organic EL display device; for example, there is a case where moisture permeating through an interface between a light-emitting layer and an electrode interferes with injection of an electron, causing occurrence of dark spots and corrosion of the electrode. To solve this problem, methods for preventing or removing the influence of moisture or a like by sealing the organic EL device hermetically are proposed. To prevent the influence of moisture, the organic EL device is put into a container being impermeable to moisture and is then enclosed together with nitrogen gas hermetically. Moreover, to remove the influence of moisture, a hygroscopic agent is enclosed into the moisture-impermeable container in which the organic EL device and the nitrogen gas are enclosed together.
FIG. 8 is a cross-sectional view of a conventional organic EL display panel in a sealing cap of which a hygroscopic agent is enclosed hermetically in order to remove an influence of moisture, which is disclosed in Japanese Patent Application Laid-open No. Hei 9-148066 (hereinafter referred to as a xe2x80x9cfirst conventional examplexe2x80x9d). As shown in FIG. 8, the organic EL display device of the first conventional example is mainly constructed of a transparent glass substrate 51, an organic EL layer-stacked body 55 composed of a transparent electrode 52 (as an anode) made from ITO (Indium Tin Oxide) or a like, an EL light-emitting layer 53 made from an organic EL material or a like and a counter electrode (as a cathode) 54, each being stacked in this order, a glass sealing can 56 to seal the organic EL layer-stacked body 55 and a drying body 57 composed of a hygroscopic agent adhering to an inside surface of the glass sealing can 56. To enclose the above drying body 57 in the glass sealing can 56, two methods are available; one in which a hygroscopic compound is solidified to produce a formed body which is then fixed in the glass sealing can 56 and another in which the hygroscopic compound is put into an air-permeable bag which is then fixed in the glass sealing can 56.
FIG. 9 is a cross-sectional view of another conventional organic EL display panel in a sealing cap of which a hygroscopic agent is enclosed hermetically, which is disclosed in Japanese Patent Application Laid-open No. Sho 61-96695 (hereinafter referred to as a xe2x80x9csecond conventional examplexe2x80x9d). As shown in FIG. 9, the organic EL display panel in the second conventional example is same as that in the first conventional example in that an organic EL device 62 formed on a glass substrate 61 is sealed hermetically by a sealing cap 63. However, the organic EL display panel in the second conventional example differs from that in the first conventional example in that, instead of the drying body 57 employed in the first conventional example, a composite film 64 formed by making a composite substance composed of zeolite serving as the hygroscopitc agent, a carbon powder serving as a light-shielding substance, a light-absorbing substance and an organic resin serving as a binder, into a film-like material, is stuck to an inside surface of the sealing cap 63. By configuring as above, an attempt has been made to implement the organic EL display panel having a tolerable life characteristic and contrast and being readily manufactured.
However, in the first conventional example, if the method in which the hygroscopic compound is solidified by using a binder to produce the formed body is employed when the drying body 57 is enclosed in the glass sealing can 56, since an exposed surface area of the hygroscopic agent is made small, it causes a decrease in hygroscopic capability and, since mechanical strength of the formed body is required to some extent, the drying body 57 is not allowed to be thinner. Therefore, the organic EL display device of the first conventional example is not suitable for application for a thin-type organic EL display. Moreover, in the organic EL display device of the first conventional example, if the method in which the hygroscopic compound is put into the air-permeable bag which is then fixed in the glass sealing can 56 is employed, it is difficult to give a fixed shape to the drying body 57 because it is contained in a bag having no definite shape and, when the organic EL display panel is put in an inclined state, the drying body 57 containing the hygroscopic agent easily moves and leans, causing a touch with the organic EL layer-stacked body 55 which leads to deterioration of the organic EL layer-stacked body 55 by an external force.
Moreover, in the second conventional example, if the composite film 64 is peeled off from the sealing cap 63, it comes in touch with the organic EL device 62, causing damage to the EL device 62. Since hygroscopic agent, carbon powder and binder are mixed to produce the composite film 64, there is a risk that a function of the hygroscopic agent itself and/or a function of the light-shielding substance itself cannot be sufficiently implemented. Additionally, when components contained in the binder being an organic resin are partially left unreacted, the organic EL device is adversely affected by them.
In view of the above, it is an object of the present invention to provide an organic EL display panel which is capable of reliably holding a hygroscopic agent in its sealing cap in a manner so as to be stuck in a uniform and thin state and of being easily manufactured and of being configured to be of a thin-profile type, without sacrificing light-emitting characteristics and display contrast, and a method of manufacturing a same.
According to a first aspect of the present invention, there is provided an organic EL display panel including:
a transparent insulating substrate;
an organic EL device formed on the transparent insulating substrate;
a sealing cap to make up sealed space hermetically containing the organic EL device in cooperation with the transparent insulating substrate; and
wherein a hygroscopic agent is enclosed hermetically in the sealed space and disposed in a manner to be sandwiched between the sealing cap and an air-permeable sheet.
In the foregoing, a preferable mode is one wherein a gluing agent layer to which the hygroscopic agent is stuck is mounted on an inside surface of, at least, either of the sealing cap or the air-permeable sheet.
Also, a preferable mode is one wherein the hygroscopic agent is of a powder or grain type.
Also, a preferable mode is one wherein the air-permeable sheet is a dark color sheet.
Also, a preferable mode is one wherein the air-permeable sheet is an ultraviolet-ray blocking sheet.
Also, a preferable mode is one wherein the hygroscopic agent is stuck to the air-permeable sheet with an adhesive sandwiched between the hygroscopic agent and said air-permeable sheet.
Also, a preferable mode is one wherein the gluing agent layer is mounted on a main surface of the air-permeable sheet being opposite to the sealing cap and wherein the hygroscopic agent in powder or grain form is stuck to the air-permeable sheet with a region of the gluing agent layer other than its edge region sandwiched between the hygroscopic agent and the air-permeable sheet while the air-permeable sheet is bonded to the sealing cap with the edge region of the gluing agent layer sandwiched between the air-permeable sheet and the sealing cap.
According to a second aspect of the present invention, there is provided a method for manufacturing an organic EL display panel to produce the organic EL display panel provided with a transparent insulating substrate, an organic EL device formed on the transparent insulating substrate and a sealing cap hermetically containing the organic EL device to form sealed space enclosing hygroscopic agent in cooperation with the transparent insulating substrate, the method including:
a process of preparing an air-permeable sheet provided with a gluing agent layer covered with released paper on its surface;
a process of partitioning a region of the gluing agent layer into a first gluing agent region for sticking the hygroscopic agent in powder or grain form and second gluing agent region for bonding the air-permeable sheet to the sealing cap;
a process of peeling off a portion of the released paper covering the first gluing agent region to expose the first gluing agent region and sticking the hygroscopic agent in powder or grain form to the exposed first gluing agent region; and
a process of peeling off a remaining portion of the released paper to expose the second gluing agent region and bonding the air-permeable sheet with the hygroscopic agent being stuck to the sealing cap with the exposed second gluing agent region sandwiched between the air-permeable sheet and the sealing cap.
According to a third aspect of the present invention, there is provided a method for manufacturing an organic EL display panel to produce said organic EL display panel provided with a transparent insulating substrate, an organic EL device formed on said transparent insulating substrate and a sealing cap hermetically containing said organic EL device to form sealed space enclosing a hygroscopic agent in cooperation with the transparent insulating substrate, the method including:
a process of preparing an air-permeable sheet with a gluing agent layer mounted on a surface of the air-permeable sheet;
a process of partitioning a region of the gluing agent layer into a first gluing agent region for sticking the hygroscopic agent in powder or grain form and second gluing agent region for bonding the air-permeable sheet to the sealing cap;
a process of holding mold members to the second gluing agent region with the first gluing agent region being left exposed and sticking the hygroscopic agent on the exposed first gluing agent region to the first gluing agent region; and
a process of making the second gluing agent region exposed by removing the mold members and bonding the air-permeable sheet with the hygroscopic agent stuck to the sealing cap with the exposed second gluing agent region sandwiched between the air-permeable sheet and the sealing cap.
In the foregoing, it is preferable that edge portion of the gluing agent layer is used as the second gluing agent region and remaining portion of the gluing agent layer other than the edge portion is used as the first gluing agent region.
Also, it is preferable that a demarcation line is provided by giving a break to the released paper covering the gluing agent layer to partition the gluing agent region into the first gluing agent region and the second gluing agent region.
Furthermore, it is preferable that, after the air-permeable sheet to which the hygroscopic agent in powder or grain form is stuck has been bonded to the sealing cap, the sealing cap is junctioned, in an atmosphere of inert gas, to the transparent insulating substrate by using an ultraviolet setting adhesive sandwiched between the sealing cap and the transparent insulating substrate.
With the above configurations, since the organic EL display device is so constructed that the hygroscopic agent in powder or grain form is uniformly held on the air-permeable sheet using the gluing agent layer mounted to the back of the air-permeable sheet, it is possible to fabricate the organic EL display device of a thinner type and to prevent the hygroscopic agent from being moved and leaning within the sealing cap. Moreover, even when the hygroscopic agent happens to be peeled, since it is held by the air-permeable sheet, deterioration of the organic EL device can be prevented. Furthermore, since the hygroscopic agent is of the powder or grain type, a wide surface area of the hygroscopic agent is secured, thus providing a high hygroscopic efficiency and a stable light-emitting characteristic. Also, by using the dark color sheet, visible light can be absorbed, thus preventing reflection of light from the back when the organic EL display panel is ON and providing excellent display contrast.
With another configuration as above, since the air-permeable sheet with the gluing agent layer covered with the released paper is used and the region of the gluing agent layer is partitioned into two regions, one being the first gluing agent region (the region other than its edge region) used for sticking the hygroscopic agent in powder or grain form to the air-permeable sheet and the other being the second gluing agent region (edge region) used for bonding the air-permeable sheet to the sealing cap and the released paper existing inside the demarcation line is peeled off to stick the hygroscopic agent to the first gluing agent region while the released paper existing outside the demarcation line is peeled off to bond the sealing cap to a glass substrate with the second gluing agent region sandwiched between them, when the hygroscopic agent is stuck to the first gluing agent region, a trouble of adhesion of the hygroscopic agent to the second gluing region can be prevented and therefore weakening of the adhesive strength of the second gluing region to bond the sealing cap to the glass substrate can be avoided, thus enabling prompt, easy and reliable mounting of the hygroscopic agent. Moreover, by using the ultraviolet-ray blocking type air-permeable sheet, when ultraviolet-ray setting adhesive is irradiated with ultraviolet rays from the sealing cap side, the organic EL light-emitting layer being susceptible to ultraviolet rays can be protected efficiently against ultraviolet rays.